A new generation of undetectable drugs is threatening the validity of sport across the world, a BBC Sport investigation has revealed.
Athletes are able to use human growth hormone (HGH) with impunity because it does not show up in existing dope tests.
HGH SIDE EFFECTS
Life-threatening damage to heart, liver and kidneys
Mutation of fingers and toes
Increased risk of cancers
And the World Anti-Doping Agency has admitted to this website that is unlikely to be able to introduce a new test before the 2004 Olympics - meaning sportsmen in Athens will be able to take HGH and related banned substances safe in the knowledge that they will never be caught.
HGH is outlawed by the International Olympic Committee but is easily available over the internet. Its abuse is presently impossible to detect because it occurs naturally in the human body.
Dr Olivier Rabin, science director of WADA, told this website, "HGH is one of the main concerns we have. It's quite a challenge.
"There are currently six different teams in six different countries working on the detection of HGH.
"We would like to have something in place for the Olympics, but this (attempt at) detection has been going on for years. History has shown that you cannot always get tests ready on time, because science does not move forward smoothly.
"We have two teams whose studies, if successful, could be a possibility. But if there are elements that need to be fine-tuned, they will not be ready for the Games.
"The problem is that these tests need validation before they can be implemented. It has taken years to arrive where we are today."
Marathon world record-holder Paula Radcliffe is among those athletes concerned at the gaping loophole in the fight against doping.
"We don't know how big a problem it is, because we aren't doing the tests," Radcliffe told BBC Sport.
"There will always be innuendos and rumours, because until we find out, we can't know who is doing what."
Track record a worry
The omens for a successful implementation of a HGH test before next summer are not auspicious.
The IOC launched a project in 1996 called HGH 2000, which was supposed to deliver a test for the Sydney Olympics but failed.
"There were technical elements to solve, because it is a complicated matter," admits Rabin.
"We are dealing with a substance which is both endogenous (produced within the body) and exogenous (originating outside the body), and the exogenous HGH is absolutely similar to what is produced by your body.
"You need the cutting edge of science to decide what is endogenous and what is exogenous."
Rabin's concerns are shared by anti-doping campaigners across the world.
"You can pick up phases of drug use," Michelle Verroken, director of drug-free sport at UK Sport, told this website.
"Amphetamines were the drugs of the 1960s, EPO of the 1990s. Human growth hormone and human chorionic gonadotrophin are the present drugs in vogue."
John Brewer, head of human performance at the National Sports Centre in Lilleshall, told this website, "It's very, very difficult to stay ahead of the cheats.
"All the time, athletes and the shady medical characters who are advising them are always trying to stay one step ahead of the field. They are always looking for new ways of avoiding detection.
"Rumours spread like wildfire. They'll pick up in the changing-room that someone has tried something that works, and then for fear of being left behind, they'll try it to see if it works for them too.
"Because the rewards in sport at the highest level are so high, sportsmen almost become blind both to the possibility of being detected and also the potential side-effects on their body."